It seems you’ve done a correct installation 
The created shares are not on the domain controller, they are on the Nethserver that acts as domain member.
This should work:
smbclient //<nethserver ip>/characterization -U username -W <WORKGROUP>
This is a local issue on the Ubuntu but does no harm. Try to comment syslog = 0 in /etc/samba/smb.conf (at least for Debian that helped)
I prefer a static IP to avoid DHCP client problems or delays but if you get a dynamic IP from provider you have to get the IP on the red interface by DHCP. That’s fully ok.